1. Field of the Invention
The present invention relates to an internal combustion engine variable compression ratio system and, in particular, to an improvement thereof in which a piston includes a piston inner and a piston outer, the piston inner being connected to a connecting rod via a piston pin, and the piston outer, while being connected to the piston inner and having an outer end face thereof facing a combustion chamber, being capable of moving between a low compression ratio position close to the piston inner and a high compression ratio position close to the combustion chamber, the compression ratio of the engine being decreased by moving the piston outer to the low compression ratio position, and the compression ratio being increased by moving the piston outer to the high compression ratio position.
2. Background Art
Conventionally, with regard to such an internal combustion engine variable compression ratio system, there is a known system (1) in which a piston outer is screwed around the outer periphery of a piston inner, and rotating the piston outer forward and backward so that it approaches and recedes from the piston inner moves it to a low compression ratio position and a high compression ratio position (for example, Japanese Patent Application Laid-open No. 11-117779), and a known system (2) in which a piston outer is fitted in an axially slidable manner around the outer periphery of a piston inner, an upper hydraulic chamber and a lower hydraulic chamber are formed between the piston inner and the piston outer, and supplying hydraulic pressure alternately to these hydraulic chambers moves the piston outer to a low compression ratio position and a high compression ratio position (for example, Japanese Patent Publication No. 7-113330).
Depending on the running conditions of the internal combustion engine, it may be necessary for the compression ratio to be switched between three or more stages, but it is difficult to satisfy such a requirement with the above-mentioned conventional system (1) or (2). Furthermore, in the conventional system (1), since it is necessary to rotate the piston outer in order to switch the compression ratio, the shape of the top face of the piston outer is restricted by the shape of the ceiling of the combustion chamber or the arrangement of intake and exhaust valves, and it cannot be set freely.